Conventionally, a heat exchanger has been known, which includes a pair of header collecting pipes and a plurality of flat tubes connected to the header collecting pipes. Patent Documents 1 and 2 disclose the heat exchangers of this type. Specifically, in each of the heat exchangers described in Patent Documents 1 and 2, the header collecting pipes stand upright respectively at right and left ends of the heat exchanger, and the plurality of flat tubes are arranged so as to extend from the first header collecting pipe to the second header collecting pipe. Moreover, each of the heat exchangers described in Patent Documents 1 and 2 exchanges heat between refrigerant flowing inside the flat tube and air flowing outside the flat tube.
In each of the heat exchangers described in Patent Documents 1 and 2, the following is repeated: a flow of refrigerant in the heat exchanger branches into some of the flat tubes, and then such flows of refrigerant from the flat tubes are joined together. That is, a flow of refrigerant into the first header collecting pipe branches into some of the flat tubes extending toward the second header collecting pipe. After passing through the flat tubes, the flows of refrigerant are joined together at the second header collecting pipe. Then, the flow of refrigerant re-branches into the other flat tubes extending back to the first header collecting pipe.